MRI of Blood Volume and Cellular Uptake of Superparamagnetic Iron in an Animal Model of Choroidal Melanoma

Functional magnetic resonance imaging (MRI), using monocrystalline iron oxide nanoparticles (MION) as a new intravascular contrast agent, was adapted for a rabbit model of pigmented choroidal melanoma. Three-dimensionally spoiled gradient recalled sequences were used for the quantitative assessment of blood volume and cellular uptake. In all ocular tissues studied, MION reduced the T(2)-weighted signal intensity within 0.5 h and at 24 h (both p < 0.05) after the injection. In individual tumors, MION reduced the T(2)-weighted signal intensity by 46-78% within 0.5 h and by 24-48% at 24 h. In addition, MION increased the T(1)-weighted signal intensity in all tissues. T(2) yielded a higher sensitivity than T(1)-weighted images. Functional MRI with MION is a noninvasive technique with regard to the eye, permitting measurement of blood volume and cellular uptake of the contrast agent. Further study is necessary to determine the feasibility of this technique for the tumor diagnosis and evaluation of tumor viability following treatments.